The serine proteases (SP) are a large family of proteolytic enzymes that include the digestive enzymes, trypsin and chymotrypsin, components of the complement cascade and of the blood-clotting cascade, and enzymes that control the degradation and turnover of macromolecules of the extracellular matrix. SP are so named because of the presence of a serine residue in the active catalytic site for protein cleavage. SP have a wide range of substrate specificities and can be subdivided into subfamilies on the basis of these specificities. The main sub-families are trypases (cleavage after arginine or lysine), aspases (cleavage after aspartate), chymases (cleavage after phenylalanine or leucine), metases (cleavage after methionine), and serases (cleavage after serine).
A series of six SP have been identified in murine cytotoxic T-lymphocytes (CTL) and natural killer (NK) cells. These SP are involved with CTL and NK cells in the destruction of virally transformed cells and tumor cells and in organ and tissue transplant rejection (Zunino, S. J. et al. (1990) J. Immunol. 144:2001-9; Sayers, T. J. et al. (1994) J. Immunol. 152:2289-97). Human homologs of most of these enzymes have been identified (Trapani, J. A. et al. (1988) Proc. Natl. Acad. Sci. 85:6924-28; Caputo, A. et al. (1990) J. Immunol. 145:737-44). Like all SP, the CTL-SP share three distinguishing features: 1) the presence of a catalytic triad of histidine, serine, and aspartate residues which comprise the active site; 2) the sequence GDSGGP which contains the active site serine; and 3) an N-terminal IIGG sequence which characterizes the mature SP.
The SP are secretory proteins which contain N-terminal signal peptides that serve to export the immature protein across the endoplasmic reticulum and are then cleaved (von Heijne (1986) Nuc. Acid. Res. 14:5683-90). Differences in these signal sequences provide one means of distinguishing individual SP. Some SP, particularly the digestive enzymes, exist as inactive precursors or preproenzymes, and contain a leader or activation peptide sequence 3' of the signal peptide. This activation peptide may be 2-12 amino acids in length, and it extends from the cleavage site of the signal peptide to the N-terminal IIGG sequence of the active, mature protein. Cleavage of this sequence activates the enzyme. This sequence varies in different SP according to the biochemical pathway and/or its substrate (Zunino et al, supra; Sayers et al, supra). Other features that distinguish various SP are the presence or absence of N-linked glycosylation sites that provide membrane anchors, the number and distribution of cysteine residues that determine the secondary structure of the SP, and the sequence of a substrate binding sites such as S'. The S' substrate binding region is defined by residues extending from approximately +17 to +29 relative to the N-terminal I (+1). Differences in this region of the molecule are believed to determine SP substrate specificities (Zunino et al, supra).
The discovery of a new serine protease precursor and the polynucleotides encoding it satisfies a need in the art by providing new diagnostic or therapeutic compositions useful in the treatment or prevention of immune disorders and cancer.